Electrolytic hydrodimerization



United States Patent 3,545,006 ELECTROLYTIC HYDRODIMERIZATION Arabinda N. Dey, Arlington, Mass., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed May 25, 1967, Ser. No. 641,175

Int. Cl. C07b 3/06 US. Cl. 204-74 4 Claims ABSTRACT OF THE DISCLOSURE In the hydrodimerization of olefinic compounds, such as in the production of adiponitrile by electrolytic hydrodimerization of acrylonitrile, improved results are obtained by mixing some of the dimerized product with the olefinic compounds fed to the electrolytic cell. In the production of adiponitrile, the formation of bis-Z-cyanoethylether is suppressed and current efliciency is increased.

BACKGROUND OF THE INVENTION It is known that adiponitrile can be produced by electrolytic hydrodimerization processes wherein acrylonitrile is fed into an electrolytic cell utilizing an aqueous electrolyte. Nascent hydrogen evolved at the cathode reacts with the acrylonitrile to form adiponitrile. Electrolytic cells commonly utilized for this purpose employ some sort of diaphragm dividing the electrolytic cell into anode and cathode compartments, and the acrylonitrile is fed into the cathode compartment in various ways. In addition to the formation of adiponitrile, various byproducts can be formed resulting in a lower yield of adiponitrile. The chief byproducts usually formed are propionitrile and biS-Z-cyanoethyl ether.

A method for producing adiponitrile 'by electrolytic hydrodimerization is described in the copending application by George T. Miller entitled, Hydrodimerization With Wicking Type Electrode, S.N. 638,484, filed May 15, 1967, now US. 3,492,209 wherein acrylonitrile or a liquid comprising acrylonitrile is flowed as a film across the face of the cathode, utilizing an electrolyte which has a small solubilizing elfect on acrylonitrile, preferably a strong acid such as a 1 to 5.5 molar solution of sulfuric acid or phosphoric acid. Another electrolytic process for producing acrylontirile is described in my copending application filed of even date herewith entitled Hydrodimerization With Porous Cathode, S.N. 641,345, filed May 25, 1967, in which process acrylonitrile is fed through a porous cathode structure onto the cathode surface, where it reacts. The size of the pores or openings through which the acrylonitrile passes are such that the surface tension elfects at the interface between the acrylonitrile and electrolyte at the cathode face are sufficient to overcome the hydrostatic pressure of the electrolyte, so that the acrylonitrile will seep through the electrode over the entire electrode surface.

These and other methods for hydrodimerization may also be used for electrolytic coupling of a variety of alpha, beta-olefinic compounds. In these electrolytic processes, an undesired byproduct is the ether formed by reaction of the olefinic reactant with water, for example, bis-Z-cyanoethyl ether from acrylonitrile.

DESCRIPTION OF THE INVENTION I have now discovered that the ether byproduct formation can be suppressed and the current efliciency increased by feeding some of the desired hydrodimerization or coupling product, along with the olefinic reactant, to the electrolytic cell. Thus, in the hydrodimerization of acrylonitrile to produce adiponitrile, I feed a mixture of adiponitrile and acrylonitrile to the electrolytic cell.

My invention will be illustrated by the following.

3,545,006 Patented Dec. 1, 1970 EXAMPLE Three experiments were carried out for the hydrodimerization of acrylonitrile to form adiponitrile in an electrolytic cell in which anode and cathode compartments were separated by a fritted glass diaphragm. The anode was a platinum sheet and hollow porous cathodes were employed. In the three experiments carried out, the porous cathode used in experiment number 1 was made of sintered stainless steel; in Experiments 2. and 3, the the cathode was porous carbon. In each case, the acrylonitrile was fed into the interior of the porous cathode and seeped through the pores to the surface, where it reacted. The electrolyte in both the anode and cathode compartments of the cell was a ten percent aqueous solution of sodium sulfate. The organic liquid fed into the cathode rose up along the cathode face to the surface of the electrolyte and was separated from the electrolyte at the con-.

Experiment 1 2 3 Feed: Part by weight of adiponitrile to one part acrylonitrile None 0. 05 0. 11 Ampere-hours 2. 0 1. 5 2. 27 Current efllciency, percent 10 44 Product: Parts BCE* to one part adiponitrile 0.35 0.07 0.009

*Bis-Z-eyanoethyl ether.

In practicing my invention, the proportion of adiponitrile to acrylonitrile in the mixture fed to the cell may be varied over a considerable range, such as from about 0.01 to one part by weight of adiponitrile to one part of acrylonitrile. I generally prefer to utilize from 0.05 to 0.5 part of adiponitrile to one part by weight of acrylonitrile. If desired, the mixture may be diluted with one or more other organic liquids which are substantially inert to the electrolyte and the electrolytic reaction, for example, aliphatic hydrocarbons having 5 to 14 carbon atoms, including hexanes, octanes and light petroleum fractions.

Any aqueous solution which does not react directly with the olefinic reactant and which has good electrical conductivity may be utilized as the electrolyte. I prefer, however, to use electrolytes which have a low solubility for the olefinc reactant, particularly those which will dissolve not more than 10 percent by weight of said reactant. Such electrolytes include the alkali metal salts of strong acids for example sodium and potassium sulfates, phosphates and chlorides, such as phosphoric acid, sulfuric acid and hydrochloric acid. I prefer to utilize a 1 to 5.5 molar solution of sulfuric acid or phosphoric acid. Other electrolyte solutions dissolving more than 10% of the olefinic reactant can be used, but such usually require careful and constant adjustment of the pH to avoid the formation of excessive amounts of undesired byproducts.

The temperature of the electrolyte and the current density may vary over wide ranges. The temperature may vary from as low as 5 degrees centigrade up to the boiling point of the reactant. I prefer, however, not to exceed a temperature of around 70 degrees centigrade when acrylonitrile is the reactant. The current density may vary from about 5 to 200 amperes per square foot. Generally, a current density of around 50 amperes per square foot will be satisfactory.

In addition to the electrolytic hydrodimerization of acrylonitrile to adiponitrile, my invention is useful for accomplishing the electrolytic reductive coupling of a great many other olefinic compounds, particularly those having alpha, beta-unsaturation associated with a reactive group such as cyano, carboxylate or amido groups.

Such compounds may be hydrodimerized, or other product of reductive coupling may be produced by subjecting mixtures of different olefinic compounds to electrolysis by my process. Examples of such compounds include methacrylonitrile, l-chloroacrylonitn'le, .l-fluoroacrylonitrile, crotonitrile, fumaronitrile, mucononitrile, 2-pen-.

tenenitrile, 2 methylenebutyronitrile, l propylacrylonitrile, acrylamide, l-chloroacrylamide, 1-fiuoroacrylamide, crotonamide, N,N'-dimethyl crotonamide and other crotonamides, methacrylamide, acrylic acid, methacrylic acid, l-fluoroacrylic acid, crotonic acid, fumaric acid, cinnamic acid, methyl methacrylate, ethyl acrylate, butyl acrylate, ethyl cinnamate, monopropyl fumarate, ethyl crotonate, ethyl citraconate, l-cyanobutadiene, lcyanocyclohexene, 1 cyano 3 ethyl-cyclohex-l-ene, 2- ethoxyacrylamide, N,N-diethylacrylamide and ethyl 2- ethoxyacrylate.

My invention further is useful for the reductive coupling of the above types of compounds with various olefinic ketones such as methyl vinyl ketone, mesityl oxide, etc., described in US. Pat. 3,193,479, and for the coupling reactions with olefinic compounds having the pyridine ring, as disclosed in US. Pat. 3,218,245. It also can be used for the reductive coupling of olefinic phosphonates, phosphinates, phosphine oxides and sulfones disclosed in US. Pat. 3,249,521.

What is claimed is:

1. In an electrolytic process for producing a hydrodimerization product of an a,[3-olefinic compound comprising applying a decomposition voltage between an anode and a cathode through an aqueous electrolyte While feeding said a, 3-olefinic compound to the active surface of said cathode, wherein said aqueous electrolyte is capable of dissolving not more than 10% by weight of said a,,B-olefinic compound, the improvement which comprises feeding to said active cathode surface from 0.01 to 1 part of said hydrodimerization product per part by weight of said 0a,,B-0l6fit1i0 compound.

2. The process of claim 1 in which said a,fi-olefinic compound is acrylonitrile and said hydrodimerization product thereof is adiponitrile.

3. The process of claim 1 in which the electrolyte is a 1 to 5.5 molar solution of sulfuric acid.

4. The process of claim 1 in which the eletcrolyte is a 1 to 5.5 molar solution of phosphoric acid.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner R. L. ANDREWS, Assistant Examiner 

